Thermostatic circuit control



1,623,568 Apnl 1927' A. E. WHITTIER THERMOSTATIC CIRCUIT CONTROL Fi led Sept. 4, 1925 I Patented Apr. 5, 1927.

ALBERT E. WHITTIER, F BRISTOL, CONNECTICUT.

THERMOSTATIC CIRCUIT CONTROL.

Application filed September 4, 1925. Serial No. 54,409.

This invention relates to those devices which are more particularly designed for controlling the current in the circuits of electrically heated apparatus, such for 1nstance as electric ranges and ovens.

The object of the invention is to provide a simple and cheap thermostat of this character which may be readily adjusted to control the heat closely to the desired degree,

and clearly indicate the maximum and mm:-

mum degrees at which the circuit conditions will be changed.

.This object is attained by providing a unimy instrument having a simple thermo- 3 staticstrip, a pointer actuated thereby and a dial graduated to show the range of degrees of heat for which the instrument is designed, with a circuit control having normally stationary but easily adjustable contacts and circuit connecting terminals, and a contact movable between the stationary con tracts for making and breaking connection therewith, said movable contact having a circuit connecting terminal and adapted to be engaged and moved by the thermostatically controlled pointer for establishing the circuit connections according to the setting of the instrument and the desired tempera-' ture conditions, all of said elements being en- 1 closed in a casing designed to be conveniently applied to the wall of the oven or other apparatus the temperature of which is to be controlled.

In the'accompanying drawings Fig. 1 shows a front view of an apparatus which embodies the invention. Fig. 2 shows a back view of the same. Fig. 3 is a central section taken on the plane indicated by the dotted line 33 on Fi 1. Fig. 4 is a back view of the circuit c anger. Fig. 5 is a side view of the circuit changer. Fig. 6 is a diagram illustrating an electric circuit for which thedevice is particularly adapted. In this view the movable contact of the circuit control is indicated as in the position occupied when the heating circuit is closed. Fig. 7 is a similar view with the movable contact. in the position occupied when the current is off. Fig. 8 is a view with the contacts as related when the current is on and the temperature has risen above the predetermined minimum.

The elements of this structure are shown as enclosed in a cylindrical case 1 that has an annular plate 2 with fasteningears 3. Over the front of the case is a glass cover 4 held in place by a cap ring 5. When put in position for use the cylinder is passed through the wall of the oven and the back plate fastened to the inner surface of the oven wall. Extending across the case and separating the interior into two compartments is a dialplate 6, on the front face of which are the graduations that indicate the degrees of temperature for which the instrument is designed. Rotatably supported by the dial plate-is an arbor 7-. A pointer 8 is fastened to this arbor in front of the dial so as to swingover the graduations, and an arm 9 is fastened to the arbor back of the plate.

One end of the-curved theremostatic strip 10 is connected with this arm and the other end of the strip is connected with a stud 11 on the back of the dial plate. Changes in temperature acting upon, the strip cause the pointer to turn in the usual manner of instruments of this character.

Inthe front compartment of the case is a plate 12 that has an opening through which the graduations on the dial may be observed. A block of insulation 13 is pivotally mounted on the back of this plate. This insulating block may be rotated by means of the thumb piece 4. Fastened to one edge of the block is a contact strip 15 provided at one end with a contact screw 16 and at the other end with a binding screw 17 to which a circuit wire may be connected. Fastened to the other edge of the insulating block is a conducting strip 18 having contact screw 19 at one end and binding screw 20 at the other end. Attached to the front and back faces of the insulating block are conducting ears 21. One of these ears isprovided with a terminal binding 'screw 22. Between the ears one end of a conducting finger 23 is hinged in such a way that itsfree end may swing into and out of engagement with the contact screws 16 and 19. An insulating piece 24 is fastened to the finger in such manner that it extends into the path of the pointer and is adapted to be engaged by the pointer as it moves upward over the dial. from a lower to higher position as the heat increases. Attached to the finger 23 is a projecting piece 25 which acts as a counterbalance and tends to swing the finger downward across the scale and keep it normally in contact with the screw 16 on the low side but allows the pointer to push the finger away from the screw.

When this device is fastened in the wall of an electrically heated oven and the circuit wires -are connected the thumb piece is turned and the block carrying the conducting strips set so as to bring the space between the contact screws over the graduation which indicates the temperature to which it is desired to have-the device function, that is, the temperature to be maintained in the oven. The counterbalance keeps the swinging finger, as stated, against the screw on the low side and the circuit wires are so connected that under this condition the circuit through the heating unit is closed. As the temperature rises the pointer moves up over the scale. When it reaches the insulating piece on the finger the pointer carries the finger upward with it awayfrom the contact screw on the low side. Continned rise of the temperature and. upward movement of the pointer finally carries the finger into engagement with the contact screw on the high side and the circuit to the heating unitis then opened. This instrument is desirably used in connection with a commonly known Dunn relay control system, as illustrated by the diagrams. In these diagrams 23 indicates the swinging contact finger, 16 the low contact screw, 19 the high contact screw, and 22 the terminal binding screw connection with the finger, of the instrument which embodies the present invention. -With the connections to the re lay control system mentioned, as illustrated, and the finger engaged with the low contact screw, as illustrated in Fig. 6, the circuit is closed through the circuit breaking relay 26 and current flows to the heating unit 27. As the temperature rises and the finger is pushed by the pointer away from the low contact screw the current still passes through the relay keeping it closed andthe heating unit in circuit, until the finger engages the .high contact screw at whichtime the relay is shunted and opens, cutting out the heating unit, as indicated in Fig. 7. The circuit containing the heating unit remains open as the temperature drops until the-finger again engages with the low contact screw. In other words with the particular circuit breaking relay control indicated, the load goes on when the finger touches the low contact and remains on until the finger touches the high'contact, and the load remains ofi until the finger again touches the low contact.

The instrument is cheap to construct, easy to locate in place of use, simple to connect in the circuit, readily adjustable to maintain the desired degree of heat, and efiicient in that it controls the temperature to within a very slight difference between minimum and maximum degrees of heat.

The invention claimed is 1 A thermostatic circuit control comprising a casing-containing a dial, a thermostatic strip, a pointer movable over the dial and controlled by said strip, normally stationary conductors, means for adjusting said conductors over the dial, a finger intermediate said. conductors and adapted to be engaged and moved by the pointer in one direction from contact with one of the stationary conductors to contact with the other stationary conductor, means independent of said pointer for moving the finger in the opposite direction, and means for connecting circuit wires to said conductors and finger.

2.- A-thermostatic circuit control comprising a casing containip a dial, a thermostatic strip, a pointer mova le over the dial and controlled by said strip, conductors normally stationary but rotatably adjustable over the dial, means for rotating said conductors, a hinged finger rotatable with said conductors and adapted to be engaged and moved by the pointer from engagement with one of the said conductors to the other conductor, and means for connecting circuit wires to said conductors and finger. 3. A thermostatic circuit control comprismg a casing containing a dial, a thermostatic strip, a pointer movable over the dial and controlled b said strip, normally stationary but rotata ly adjustable conductors, a hinged finger adjustable with said conductors and adapted to be engaged and moved by the pointer from one of said stationary conductors to the other, a counterbalance normally retaining the finger in engagement with one of said conductors, and means for connecting circuit. wires to said conductors and finger.

4. A thermostatic circuit control comprising a casing containing a dial, a thermostatic strip, a pointer-movable over the dial and controlled by said strip, a pivoted finger adapted to be engaged and moved up by the pointer as the temperature rises, a conductor normally engaged by the finger at the lower limit of its movement, gravity controlled means acting oppositely to the pointer and tending to move' the finger downward into engagement with said conductor, a conductor adapted to be engaged by the finger at the upper limitof itsmovement, and means for connecting circuit wires to said conductors and finger.

5. A thermostatic circuit control comprising a casing containinga dial, a thermeing finger mounted on and retateble with static strip, a ointermovable ever the dial said block intermediate seid pair. of com and controlle by said strip, a rotatably ductors and adapted to be engaged and W mounted insulating block with means for moved by the pointer from one cemuetor to Ietating said block, a pair of conductors the other,

fastened to said block and, hearing Contact;

screws and binding screws, ami e conduct ALBERT E. VVHITTIER. 

